What's the deal with this extreme low-calorie lifestyle that supposedly elongates your life? It's not a temporary diet but a permanent way of eating. It sounds very suspiciously like an eating disorder and I'm wondering what the health benefits of this actually are. - Olivia, CA

Christine Palumbo, RD:
Although prolonged calorie restriction is known to increase life span in mice, researchers arenít sure if that also applies to humans. Proponents aim to maximize their nutrients on fewer calories. The idea is to cut calories by 25 to 30% in order to add years to your life.

A preliminary study published in the April 5, 2006 issue of the Journal of the American Medical Association studied humans whose diets were calorie restricted by 25% (through diet alone or diet plus exercise) for six months. The 48 overweight people measured lower levels of DNA damage, which is thought to be a significant factor in the aging process. Other results include a reduction in fasting insulin level and core body temperature (both biomarkers of longevity). Stay tuned for longer studies to determine if calorie restriction actually does lengthen human lifespan.